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In Cixin Liu’s Remembrance of Earth's Past trilogy, why does it take the Trisolaran fleet 400 years to reach the solar system if it can achieve a speed of 1/10 the speed of light, given that Alpha Centauri is only 4.4 light years away? Even accounting for a 1g acceleration then deceleration, wouldn’t it take only 50 years or so?

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  • Simple arithmetic would suggest that a vessel traveling at 0.1 the speed of light would take at least 40 years to cover a distance of 4 light years or more, and that's assuming it traveled at its top speed constantly from start to finish. If the journey actually took 400 years rather than 40, it would suggest the vessel was only moving at around 0.01 the speed of light rather than 0.1. Not sure any of this is on-topic for this site though. – LogicDictates Apr 6 at 14:14
  • In the novel it is stated that the Trisolaran feet can travel at 1/10 the speed of light, hence my confusion. – Antoine Conze Apr 6 at 14:16
  • I haven't read those books, but perhaps the 400 years figure is some sort of typo or miscalculation on the author's part then, and the correct journey time was approximately 40 years, rounding down to one significant figure. It does seem noteworthy that the actual figure given (400 years) is precisely 10 times what it should be (if the given speed is correct), and that the numerical inconsistency can be rectified by simply removing a zero from 400. – LogicDictates Apr 6 at 14:34
  • @LogicDictates It is not an error; it is a major part of the plot. (The actual figure is something like 450 years, IIRC.) – DavidW Apr 6 at 14:38
  • @AntoineConze Is there any evidence that the Trisolaran fleet accelerated at 1g? – DavidW Apr 6 at 14:54
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This apparent paradox is addressed explicitly by Liu when Ye Wenjie is being interrogated. Just as the OP asks:

INTERROGATOR: Then I have a question. If the Trisolaran Fleet that had been launched is capable of flight at one-tenth the speed of light, it should take only forty years to reach the solar system. So why do you say that it would take more than four hundred years?

The answer is:

YE: Here’s the thing. The Trisolaran Interstellar Fleet is composed of incredibly massive spaceships. Accelerating them is a slow process. One-tenth the speed of light is only their maximum speed, but they cannot cruise at this speed for long before decelerating as they approach the Earth. Also, the source of propulsion for the Trisolaran ships is matter-antimatter annihilation. In front of each ship is a large magnetic field shaped like a funnel to collect antimatter particles from space. This collection process is slow, and only after a long wait can it gather enough antimatter to allow the ship to accelerate for a brief period. Thus, the fleet’s acceleration occurs in spurts, interspersed by long periods of coasting to collect fuel. This is why the time it takes the Trisolaran Fleet to reach the solar system is ten times longer than the flight time of a small probe.

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  • Thank you very much! – Antoine Conze Apr 6 at 15:29
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    @Antoine Conze - Please don't forget to mark the answer as accepted by clicking on the check mark beneath the voting buttons. – LogicDictates Apr 6 at 15:39
  • @DavidW interstellar space is not empty: en.wikipedia.org/wiki/Interstellar_medium – Jan Spurny Apr 6 at 15:46
  • @LogicDictates trying to but the system won't let me as I originally posted the OP anonymously, my mistake :( – Antoine Conze Apr 6 at 15:48
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    @Antoine Conze - Please try to merge the two accounts by following the instructions given here. If it works, you'll then be able to accept the answer. – LogicDictates Apr 6 at 15:52

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